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Chapter 12. Hydraulics

Table of Contents

12.1. Green + yellow systems low pressure
12.2. Blue + yellow systems low pressure
12.3. Green + blue systems low pressure
12.4. Green system low pressure
12.5. Yellow system low pressure
12.6. Blue system low pressure
12.7. Engine driven pump low pressure
12.8. Electric pump low pressure or overheat
12.9. Low reservoir air pressure
12.10. Reservoir overheat
12.11. Low reservoir fluid level
12.12. PTU fault
12.13. RAT fault

12.1. Green + yellow systems low pressure

It may be possible to recover the yellow system using the yellow electrical pump. Systems lost because of low air pressure in the reservoir will be recoverable at lower altitudes. Systems lost due to reservoir overheats may be usable for the approach once they have cooled down.

Roll control is available from ailerons and spoiler 3. Pitch control is available from the elevators, but the THS is frozen. Yaw damping is lost. Slats are available, but slow. Flaps are frozen. Control law reverts to alternate law without stability protections. The autopilots are lost.

The gear must be gravity extended, but due to the frozen THS this must be delayed until VAPP is achieved in CONF 3. Furthermore, transition to CONF 3 must be achieved in accordance with Section 5.6, “Flaps and/or slats fault/locked” due to the flaps being frozen. Transition to direct law on gear deployment adds to the fun, especially as pitch trim is unavailable.

Cat 2 and 3 capability is lost. The landing will be CONF 3, most probably with only the slats deployed; the flare attitude will be abnormal. There will only be one spoiler (#3), no reversers, accumulator only braking and no nose wheel steering. Hence required landing distances almost triple.

The go around, in some ways, is exceptionally straightforward. The gear cannot be raised and the configuration should be maintained. Due to the frozen stabiliser, a speed close to VAPP should be flown.[38] As long as the flaps are frozen at zero, the slats can be retracted for a subsequent diversion; fuel flow will be approximately 3 times normal due to the extended gear. If flaps are not at zero, fuel flow will be up to 4 times normal.

A paper summary is available in section AEP.HYD of the QRH, and this should be applied once all ECAM actions are completed.

[HYD G + Y SYS LO PR, QRH AEP.HYD, FCOM PRO.AEP.HYD]

12.2. Blue + yellow systems low pressure

It may be possible to recover the yellow system using the yellow electrical pump or the blue system using the RAT. Systems lost because of low air pressure in the reservoir will be recoverable at lower altitudes. Systems lost due to reservoir overheats may be usable for the approach once they have cooled down.

Roll control is provided by ailerons and spoiler 5, pitch control by the THS and left elevator. Slats and flaps are available at reduced rate. The autopilots are lost but Normal law is retained. Speedbrake is unavailable.

Cat 2 and 3 capability is lost. Landing distances are increased due to loss of spoilers 2, 3 and 4 and loss of #2 reverser. Approach configuration is normal apart from slow flaps and slats and gravity gear extension (protects green system). Nose wheel steering is lost.

Gear cannot be retracted on go-around. Fuel burn for a subsequent diversion will be significantly greater (approx factor 3 times normal); see Section 8.6, “Flight with landing gear extended” for further details.

A paper summary is available in section AEP.HYD of the QRH, and this should be applied once all ECAM actions are completed.

[HYD B + Y SYS LO PR, QRH AEP.HYD, FCOM PRO.AEP.HYD]

12.3. Green + blue systems low pressure

If the blue system has been lost due to the loss of its electrical pump, it may be recovered by deploying the RAT. Systems lost because of low air pressure in the reservoir will be recoverable at lower altitudes. Systems lost due to reservoir overheats may be usable for the approach once they have cooled down.

Roll control is provided by spoilers 2 and 4 only. Use of speedbrake would therefore lead to loss of roll control. Pitch control is available from the starboard elevator; the THS remains available. Due to the limited control surfaces available, the aircraft will be slightly sluggish. The slats are frozen, but flaps are available. Control law reverts to alternate law without stability protections. The autopilots are lost. The approach will be flown with the autothrust off.

Due to the frozen slats, configuration changes must be carried out in accordance with Section 5.6, “Flaps and/or slats fault/locked”. The gear must be gravity extended; to benefit from the improved elevator response available in direct law, this is done at 200kt. Manual trim will be available.

Cat 2 and 3 capability is lost. The landing will be CONF 3. Two spoilers per wing are available, reverser 2 is available, alternate braking is available and nose wheel steering is available. Landing distances approximately double.

Go around is straightforward – the gear cannot be retracted and the flap configuration should be maintained. Simply select VFE‑10. For diversion, the flaps can be retracted. With the gear remaining down, fuel burn will increase by a factor of approximately 3 if the slats are at zero or up to approximately 3½ if they are extended.

A paper summary is available in section AEP.HYD of the QRH, and this should be applied once all ECAM actions are completed.

[HYD G + B SYS LO PR, QRH AEP.HYD, FCOM PRO.AEP.HYD]

12.4. Green system low pressure

The major lost systems are normal landing gear operation (gravity extension is available but gear retraction is not) and the normal brake system, including the autobrake (alternate braking is available). Landing distance will be increased due to loss of two spoilers per wing and reverser 1. Flap and slat deployment will be slow.

[HYD G SYS LO PR, FCOM PRO.AEP.HYD]

12.5. Yellow system low pressure

It may be possible to recover the yellow system by using the yellow electric pump.

Two spoilers per wing and reverser 2 are lost, so landing distance will increase slightly. Nose wheel steering is lost. Flap deployment will be slow. As the alternate braking system is only available through the brake accumulator, ensure there is sufficient pressure when the parking brake is set.

[HYD Y SYS LO PR, FCOM PRO.AEP.HYD]

12.6. Blue system low pressure

One spoiler per wing will be lost but this has negligible effect on landing distance. Slats will be slow to deploy. Deployment of the RAT is not recommended unless another system is lost. If the system is lost due to low reservoir level, emergency generation capability is lost.

[HYD B SYS LO PR, FCOM PRO.AEP.HYD]

12.7. Engine driven pump low pressure

Turn off the affected pump. The PTU will pressurise the affected system.

[HYD G(Y) ENG 1(2) PUMP LO PR, FCOM PRO.AEP.HYD]

12.8. Electric pump low pressure or overheat

Turn off the affected pump. In the case of an overheat, the pump may be re-engaged for the approach providing the relevant FAULT light on the overhead panel has extinguished.

[HYD Y(B) ELEC PUMP LO PR(OVHT), FCOM PRO.AEP.HYD]

12.9. Low reservoir air pressure

Loss of air pressure to a hydraulic reservoir may lead to pump cavitation and hence fluctuating pressures. If this occurs, turn off the affected pump, and if applicable, turn off the PTU. Cavitation reduces with altitude, so it may be possible to reinstate the system during the descent.

[HYD G(Y)(B) RSVR LO AIR PR, FCOM PRO.AEP.HYD]

12.10. Reservoir overheat

Turn off all affected pumps and if applicable, turn off the PTU. The system should be reinstated for the approach if it has cooled sufficiently. This is indicated by the FAULT light going out on the overhead panel.

[HYD G(Y)(B) RSVR OVHT, FCOM PRO.AEP.HYD]

12.11. Low reservoir fluid level

Turn off all affected pumps and, if applicable, turn off the PTU. The affected system is not recoverable. In the case of low reservoir level in the yellow system, it is possible that the fluid from the brake accumulator may also be lost. This usually occurs within 10 minutes of the initial warning. Without the brake accumulator, the parking brake is not available, so chock the aircraft before shutting down engine 1.

[HYD G(Y)(B) RSVR LO LVL, FCOM PRO.AEP.HYD]

12.12. PTU fault

In flight this indicates that either the green or yellow system is low on fluid and has low system pressure. The PTU must be turned off to prevent overheating the supplying system.

[HYD PTU FAULT, FCOM PRO.AEP.HYD]

12.13. RAT fault

Indicates that either the RAT is not fully stowed, pressure is present in the RAT stowing actuator or that the RAT pump is not available. No action is required.

[HYD RAT FAULT, FCOM PRO.AEP.HYD]



[38] Airbus originally suggested flying VFE‑10kt; I assume this was found to cause handling difficulties due to pitch trim not being available.